A light emitting diode (LED) can achieve high luminance emission with low power. Accordingly, it has been used as a light source for various electrical apparatuses such as a display and an illumination apparatus. Recently, in addition to a red LED and a green LED, a blue LED has been put to practical use, thus, making it possible to emit light having various colors by combining the three colors (RGB), i.e., red, green and/or blue of LEDs. Further, it is possible to arbitrarily set color temperature of the emitted light by combining an LED with a phosphor which converts a wavelength of light emitted from the LED.
Conventionally, there is known a light emitting device including a blue LED that emits blue light, a red LED that emits red light, and a sealing resin containing a plurality of phosphors which are excited by light emitted from the blue LED to emit light (see, e.g., Japanese Patent Laid-open Publication No. 2010-147306 (JP 2010-147306)). The sealing resin covers the LEDs. In the light emitting device, the plurality of phosphors have emission peak wavelengths in a wavelength range between a peak wavelength of the light emitted from the blue LED and a peak wavelength of light emitted from the red LED.
According to this configuration, light in an intermediate wavelength range between the light emitted from the blue LED and the light emitted from the red LED can be widely compensated by light emitted from the phosphors. As a result, it is possible to enhance a color rendering property of the mixed light from the light source.
In the light emitting device described in JP 2010-147306, multiple phosphors are excited by the light emitted from the blue LED having a peak wavelength on the short wavelength side of visible light to emit light. Color temperature of the light emitted from the light emitting device is changed by controlling a turn-on power of each LED. Therefore, when the turn-on power of the blue LED increases, the power of light in the intermediate wavelength range (e.g., green to orange light) emitted from the phosphors accordingly rises. Therefore, it is impossible to obtain illumination light with a sufficiently high color temperature. Consequently, a variable range of the color temperature becomes narrow.
Further, while the color temperature can be adjusted by controlling the turn-on power of the red LED in a relatively low color temperature range, it is difficult to adjust the color temperature by controlling the turn-on power of the blue LED in a relatively high color temperature range. As a result, it is difficult to smoothly vary the color temperature of the illumination light.